Electrostatic chucks are used as means to adhere and hold an object to be processed (such as a semiconductor wafer or a glass substrate) in a plasma processing chamber that performs etching, chemical vapor deposition (CVD), sputtering, ion implantation, ashing, and the like.
Methods of fabricating the electrostatic chuck include sintering a plate-like ceramic dielectric substrate, and forming an electrode on one side of the substrate by CVD, sputtering, or the like (single plate structure), or fabricating ceramic green sheets by the sheet forming method, and laminating a plurality of layers of green sheet on the top and bottom of a green sheet on which an electrode is printed (internal electrode structure). In the electrostatic chuck, an internal electrode structure is suitable, from the point of view of ensuring sufficient adhesion force and high withstand voltage.
However, after plasma processing, residues or matter generated from the semiconductor wafer or applied films adhere to the inner faces of the chamber. When plasma processing is repeatedly carried out, the residues and generated matter are gradually deposited, and eventually they peel from the inner faces of the chamber and adhere to the surface of the object to be processed such as a semiconductor wafer, a glass substrate, or the like, which causes a reduction in manufacturing yield.
Therefore, conventionally, periodically, the inside of the chamber is cleaned by plasma, and the residues and adhering matter adhering to the inner faces of the chamber are removed. In this case, in some cases, so-called waferless plasma cleaning is carried out, by processing without covering the surface of the electrostatic chuck with a dummy wafer. In waferless plasma cleaning, the surface of the electrostatic chuck is directly exposed to cleaning plasma such as O2 gas, CF4 gas, or the like during cleaning.
When waferless plasma cleaning is carried out for electrostatic chuck, particles are separated from the ceramic surface and erosion occurs at the grain boundaries, so the surface roughness increases. As a result, problems such as reduction in the electrostatic adhesion force, increase in the quantity of leakage of sealing gas, lowering in the heat transfer coefficient of the solid contact interface with the semiconductor wafer, and the like occur, and after a short period of time, it is necessary to replace the electrostatic chuck.
Therefore, Japanese Unexamined Patent Application Publication No. H10-279349 discloses a method of manufacturing an electrostatic chuck with an internal electrode structure that uses high purity alumina as the dielectric body, as a method of suppressing the change in surface roughness due to plasma irradiation by halogen gas or the like.
Japanese Unexamined Patent Application Publication No. H10-279349 discloses using a green sheet that uses alumina powder with 99.5% purity as a conductor by applying a paste including powders such as W, Mo, WC, TiC, TiN or the like.
Also, Japanese Unexamined Patent Application Publication No. H08-119720 discloses the structure of an electrostatic chuck in which a conductor made from Pd on its own or Pd including Ag of not more than 40% by weight is applied to a green sheet that uses alumina powder with purity of not less than 99.9% as the internal electrode.
However, when fabricating an electrostatic chuck with an internal electrode structure using high purity alumina green sheets, the bond between the internal electrode layer and the high purity alumina layers on the top and bottom of the internal electrode layer is weak, and separation at the boundary between the high purity alumina layer and the internal electrode layer can easily occur during processing. Therefore, in order to strengthen the bond, there is the method of adding alumina to the internal electrode layer as a common material, but in this case, the problem that the conductivity of the internal electrode is reduced by adding the alumina occurs.